Various types of arrangements have heretofore been proposed incorporating means for spraying water through gases to remove impurities therefrom and also incorporating means for filtering and recirculating the water. The British patent No. 535,484 is an early example. It has also been proposed to use similar arrangements in conjunction with cooking stoves for removing grease, as disclosed in the Baker, U.S. Pat. No. 3,100,809, for example. More recent developments are disclosed in the Costarella et al U.S. Pat. Nos. 3,628,311 and 3,731,462. The principles of operation of such arrangements have considerable potential importance especially with respect to the removal of grease which presents an environmental problem and also a fire hazard. When properly installed and serviced, they can reduce pollution very substantially and can reduce the likelihood of fire to a great extent. However, the proposed arrangements have not been widely used and have not been accessible to many potential users. The problems arise in part from the high cost of equipment, difficulties in installation, especially where space is at a premium, and difficulties in cleaning and maintenance, particularly where it is not possible to use trained personnel.